The present invention relates generally to infrared sensors and, more particularly to an infrared detector circuit providing feedback for improving sensitivity of the infrared sensing function in high ambient light operating environments.
Infrared sensors are known in the state of the art, finding many uses, including remote digital data transmission. For example, with the proliferation of portable computer apparatus, the use of infrared data communication between computers and between computers and computer peripherals has become common. The technique is particularly useful in what are now called notebook computers and palmtop personal digital assistants (PDA""s) where portability and ease of use are paramount. For example, rather than adding cables to the baggage that accompanies a typical user of a notebook computer and portable printer, it is preferable to use infrared data communication techniques for printing a document from the computer. Similarly, infrared data communications ports are being added to many desktop equipments to facilitate their accessibility by the user of a notebook computer. To that end, original equipment manufacturers (OEM) such as Hewlett-Packard Company (the assignee of the present invention), IBM Corporation, and Apple Computer, Inc., have associated to form the Infrared Data Association to standardize such communications. The Serial Infrared Link Access Protocol (IRLAP), Draft Version 5.1 (Apr. 28, 1994) has been generated by this Association.
In FIG. 1 (Prior Art), an exemplary computer peripheral, such as an HP(trademark) LaserJet(trademark) printer 101, is shown to have a serial infrared data communication port 103 as would be known in the art where it would receive data to be output in hard copy. In general, the invention can be implemented in any machine such as a computer, portable computer, PDA, computer peripheral, portable printer, test instrument, or the like, which will have occasion to interface with another machine by infrared link for the purpose of transferring data. The printer 101 will serve as an example, but no limitation on the scope of the invention is intended nor should any be implied. An infrared link status indicator 105 is positioned for design convenience where the user can determine that the link with his portable computer (not shown) has been established (e.g., when an indicator 105 light goes from red to green).
Infrared light is, of course, invisible to the naked eye. Generally, for an infrared data link to be established, each equipment involved must have a clear line-of-sight between their respective infrared ports. A major problem is that most computers are used in daylight or office lighting conditions. External, ambient light will reduce the infrared signal response of the receiver element. For example, as demonstrated by FIG. 2, an IR transmitter 201 sends infrared digital pulses 203 to an IR receiver port 103. In substantially total darkness, the HIGH-LOW IR signals may appear at the IR receiver port 103, as illustrated by FIG. 2A. However, in a high ambient light condition, e.g., outdoors on in the direct sunshine, the same IR receiver 103 may have a signal approaching or exceeding saturation and no data is transferred, as demonstrated by FIG. 2B. In other words, the receiver 103 can not discriminate enough of the IR pulses transmitted when ambient light exceeds some threshold for the specific receiver element""s operational design specifications.
There is a need for improving infrared signal control to solve said problem.
In a basic aspect the present invention provides an infrared signal detector including: an infrared sensor; a power source Vcc for activating the sensor, including a bias resistor; and a feedback loop coupled to said sensor, including a feedback bias resistor wherein the feedback bias resistor has a resistance approximately 1000 times greater than said bias resistor.
In another aspect, the present invention provides an apparatus having an infrared input port wherein the port further includes an infrared signal detector including an infrared sensor, a power source Vcc for activating the sensor, including a bias resistor, and a feedback loop coupled to said sensor, the loop including a feedback bias resistor wherein the feedback bias resistor has a resistance approximately 10000 times greater than said bias resistor.
In another aspect, the present invention provides a method for controlling sensitivity of an infrared sensor, said sensor including a biased power source Vcc, the method including: biasing the power source with a first resistor having a predetermined first resistance; and providing feedback to said sensor via a second resistor having a predetermined second resistance wherein a ratio second resistance:first resistance is approximately 10000:1.
The foregoing summary is not intended to be an inclusive list of all the aspects, objects, advantages, and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings. The drawings referred to in this specification should be understood as not being drawn to scale except if specifically annotated.